Delivery arrangement

ABSTRACT

A delivery arrangement including a conveyor and take-off mechanism for delivering a series of printed sheets onto a pile, in which nozzles are provided distributed along the width of a sheet for directing a jet of air in a direction opposite to sheet movement. A guide plate spaced under the sheet and extending upstream from the region of the nozzles serves to confine the jet. Interposed between the guide plate and the sheet path are a series of longitudinally extending friction or land members toward which the sheet is drawn during the course of transport, the jet and friction members serving, together, to decelerate the sheet as it is removed by the take-off mechanism. The guide plate is longitudinally slit at intervals to form windows defining extensive struck-out portions and intervening frames, the struckout portions, bent downwardly from the frames, being utilized to confine the jet while the intervening frames provide the frictional engagement. The nozzles are fed by a manifold which is divided into zones which are fed by separate controllable valves in accordance with the width of the sheets being handled. Such nozzle and guide plate assemblies are preferably used in successive sections of the sheet conveyor for control of the sheet during change of direction and to eliminate flutter.

United States Patent [1 1 Schuhmann et al.

[ Dec. 18, 1973 41 DELIVERY ARRANGEMENT [75] lnventorsz- SiegfriedSchuhmann; Claus Simeth;

Erich Wegel, all of Offenbach, Germany [73] Assignee: Roland Offsetmaschinenfabrik Faber & Schleicher AG 221 Filed: July 7, 1972 21 1 Appl. No.: 269,704

[30] Foreign Application Priority Data July 14, 1971 Germany P 21 35 105.3

[52] U.S. Cl. 271/183, 271/204 [51 Int. Cl B65h 29/04, B65h 29/68 [58] Field of Search 271/79 R, 79' SR,

271/68 R, 68 SR, 46, DIG. 2, 74 FC, 74 PG, 271/74 R, 74 MS, 182, 183, 204

Primary Exuminer-Evon C. Blunk Assistant Examiner-James W. Miller Att0rneyC. Frederick Leydig et a1.

[ 5 7 ABSTRACT A delivery arrangement including a conveyor and take-off mechanism for delivering a series of printed sheets onto a pile, in which nozzles are provided distributed along the width of a sheet for directing a jet of air in a direction opposite to sheet movement. A guide plate spaced under the sheet and extending upstream from the region of the nozzles serves to confine the jet. lnterposed between the guide plate and the sheet path are a series of longitudinally extending friction or land members toward which the sheet is drawn during the course of transport, the jet and friction members serving, together, to decelerate the sheet as it is removed by the take-off mechanism. The guide plate is longitudinally slit at intervals to form windows defining extensive struck-out portions and intervening frames, the struck-out portions, bent downwardly from the frames, being utilized to confine the jet while the intervening frames provide the frictional engagement. The nozzles are fed by a manifold which is divided into zones which are fed by separate controllable valves in accordance with the width of the sheets being handled. Such nozzle and guide plate assemblies are preferably used in successive sections of the sheet conveyor for control of the sheet during change of direction and to eliminate flutter.

14 Claims, 3 Drawing Figures l 58 /1 SOURCE OF PRESSUR/ZED AIR] PATENIEUUEE 18 1975 3 1 55 SOURCE OF PRESSUR/ZED A/Rj d SOURCE or PRESSURIZED A/RJ DELIVERY ARRANGEMENT In sheet delivery mechanisms associated with a lithographic press, sheets are conveyed rapidly in succession on an endless conveyor, from which the sheets are taken by a synchronized take-off mechanism having grippers which grip the sheet at the leading edge, decelerate it, and permit it to drop onto a delivery pile.

Because of the sudden deceleration at the leading edge it is possible for the body of the sheet to overtake the leading edge so that the sheet doesnot remain in a flat condition but becomes waved and folded upon itself to defeat orderly piling. Various schemes have been proposed for slowing down the sheet, including use of suction heads. In general, such devices have not been very effective since the braking force is usually limited to a small portion of the surface area and since the suction heads tend to become clogged with paper dust and require constant maintenance. I

It is an object of the invention to provide an improved sheet' delivery arrangement which overcomes the disadvantages of the prior art devices, which is effective to decelerate the body of a sheet over a substantial portion of its total area, and which tends to overcome any fluttering tendency, keeping the sheet flat and under control until safely deposited upon the delivery pile. 4

It is another object of the present invention toprovide a slow-down mechanism which is capable of acting over a wide range of delivery speed including the highest speeds achievable with a lithographic'press.

It is another object of the present invention to provide a sheet delivery arrangement which is high reliable, which is free of the clogging characteristic of prior pneumatic braking devices and which is capable of operating over long press runs without maintenance, care or attention.

It is a more detailed object of the present invention to provide a nozzle and guide plate assembly which may be employed in multiple along the sheet path and which includes provision for zoning or tailoring air discharge to the' width of the sheets being handled.

It is more specifically an object of the present invention to provide novel braking means to act upon successively delivered sheets, which not only relies upon the frictional effect of an extensive jet of air which is directed oppositely to the direction of sheet movement,

but which, in its preferred embodiment, provides engagement between the sheets and stationary friction members while nevertheless insuring light contact with the friction members so that the sheets are not smeared or defaced even where perfected printing is employed.

It is, finally, an object of the invention to provide a sheet decelerating arrangement vwhich is simple, inexpensive and compact and which may be employed universally for keeping sheets under control in a conveyor or delivery system.

Other objects 'and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which:

'FIG. 1 is a diagrammatic side elevational view of a delivery arrangement employing the present invention.

FIG. 2 is a perspective view, in partial section, showing the nozzle and guide plate assembly of FIG. 1 in somewhat enlarged form.

FIG. 3 is an end view of the nozzle and guide plate assembly showing the path of sheet travel and the direction of air flow.

While the invention has been described in connection with a preferred embodiment, it will be understood sheets 13. The chain is trained around rollers or I sprockets l4, 15 which are driven at press speed via a connection 16 from the press drive 17. Sheets 13 may be printed on either one or both sides in a suitable lithographic printing press (not shown). 1

The purpose of the conveyor is to convey sheets along a path 19 to a-position above a delivery pile 20 where the sheets are supported on a platform 21 which is suspended upon chains diagrammatically indicated at 22 forprogressive sinking movement as sheets are added to the top of the pile. To form a straight stack, a series of front guide members 23 are provided at the left-hand side of the pile and a series of rear guide members 24 are provided along the right-hand side of the pile. The means for maintaining the top of the pile at a constant'leve l by gradual lowering of the platform 21 does not form a part of the present invention and for details of the automatic level adjusting pile 20, a take-off mechanism 30 is provided. The take off mechanism does not per se form a part of the present invention, and any suitable take-off mechanism, synchronized with the arrival of the sheets, may be used, for example, that illustratedin German Pat. No. 613,007. Referring to the take-off mechanism 30 shown diagrammatically in FIG. 1, it includes grippers 31 mounted upon a reciprocated member 32 which is reciprocated by an arm 33 pivoted at 34. For oscillating the arm 33 a cam 35 is provided mounted upon the shaft of the member 15 and having a cam follower 36 in the form of a roller secured to the arm. The cam follower is maintained in contact with the cam by means of a tension spring 37. Means (not shown) are provided for releasing the grippers 12 on the conveyor chain so that the leading edge of the sheet may be gripped by the grippers 32 which rapidly decelerate the-sheet so that the leading edge is reduced to zero velocity by the time the leading edge arrives at the front pile guides 23, at which time the grippers 31 are released to allow the sheet to settle onto the top of the pile.

In accordance with thepresent invention a nozzle and guide plate assembly A is provided including an elongated nozzle,'or a series of nozzles, adjacent the pile of sheets and below the level of the sheet path connected to a source of air under'pressure so that air is directed parallel to the underside of the sheet in a direction opposite to the sheet movement. More specifically, in accordance with the invention, a guide plate is provided which extends under the sheet in the "up-v stream direction and which tends to confine the air jet from the nozzles, the guide plate being flared in the downward direction so as to bring about a gradual drop in the velocity of the jet.

Thus, referring to FIG. 3 of the drawings, an air manifold 40 is provided extending the maximum width of 5 the sheets and which is of rectangular cross section having a top surface 41, bottom surface 42, an upstream side 43 and a downstream side 44. The downstream side is suitably secured to a frame member indicated generally at 45. For the purpose of defining an elongated nozzle, or series of nozzles, pointed upstream with respect to the direction of sheet movement, a nozzle plate 50 is provided which is spaced a short distance above the topsurface 41 -of the manifold to define a limited headspace 52 so that air is ejected, in the form of a jet, through the elongated nozzle opening 53. For providing passage of the air from the manifold 40 into the headspace 52 under the nozzle plate, the manifold is formed with a longitudinal opening, or series of openings, 54. It will be understood by one skilled in this art that the nozzle opening 53 may be continuous or the opening 53, and headspace 52, may be occupied by a series of spacers to define a series of closely spaced nozzle openings which cooperate with one another to produce a jet along the width of the sheet. The term nozzle means has been used in the claims to cover both of these possibilities.

While in a simplified form of the present invention the entire manifold 40 may be pressurized, we preferably provide means for dividing up the manifold into a series of zoned compartments. Zoning may be accomplished by spaced baffles 55, only one of which is shown, with adjacent compartments being fed by separate conduits 56, (only two of which are shown) via separate air valves 57 which are connected to a source of pressurized air 58. By opening only a portion of the valves 56 the flow of air may be tailored to the width of the sheets being handled. However, it will be understood that the width of the jet need not be precisely tailored to the width of the sheets and the term extending along the width of a sheet used in the claims refers primarily to direction rather than extent.

For confining the air forming the jet so as to tend to form it into a more well-defined layer, and for causing the jet velocity to be progressively reduced, a guide plate 60 is provided which is spaced below the sheet (see FIG. 3) and which extends from the region of the nozzles in a direction upstream of sheet movement.

The guide plate 60 has a downwardly extending mounting flange or base portion 61 which. is secured to the upstream wall 43 of the manifold and an upstream extending portion 62 which is bent downwardly into curved or horn" shape to define a flaring space indicated at 63 under the sheet 13 and through which the jet of air, indicated at J, passes.

Because of the velocity of the air jet, which may vary from a minimum of, say, 60 feet per second to a maximum of, say, 600 feet per second, the pressure in the space 63 becomes just slightly less than atmospheric, which tends to draw the passing sheet 13 (see FIG. 3) downwardly in the direction of the guide plate 62. It will be understood that the discharge of air, under pressure, below the sheet does not blow" the sheet upwardly from its normal path of delivery, as might be expected, but it acts, instead, to suck the sheet downwardly into intimate contact with the jet which is travelling in the opposite direction. As a result the sheet is held down so that the air of the jet impinges on the underside of the sheet, tending to hold it back in its course of movement.

Further in accordance with the present invention a friction means is interposed between the guide plate and the travelling sheets so that, as the sheets are sucked downwardly by the jet action, the sheets are drawn into light frictional engagement which augments the direct effect of the air jet in braking the forward speed of the sheets. The friction means is preferably in the form of relatively narrow and relatively upraised lands or tongues which extend longitudinally of the path of travel of the sheets and which are bent downwardly at a shallow angle so as to form a smoothly curved frictional surface, at least a portion of which may be engaged by the underside of the sheets. Preferably, in accordance with the invention the guide plate 62 is formed, by a slitting operation, with a series of windows which are slit along three sides as indicated at 71, 72, 73. This forms struck out portions 62a which are bent downwardly and which, together, perform the jet-confining function previously described. The slits 71-73 moreover define window frames in the form of the narrow relatively upraised tongues 75 which are distributed in the width dimension of the sheet and which are interconnected, at the ends, by an apron 76. The apron 76 may be slotted as indicated at 77 for the securing, if desired, of sheet guide belts or the like.

By controlling the air flow through the valves 57 the degree of braking effect may be varied from a low setting, where the impingement of air alone on the underside of a sheet serves to decelerate it, to a higher velocity in which the sheet is drawn into contact with the tongues 75, the degree of engagement depending upon the velocity and upon the length and degree of curvature of the tongues 75 as well as the struck-out portions 62a which guide the air. The impingement of the air jet upon the underside of the sheet has a steadying as well as decelerating effect upon the sheet. Control of the sheet is still further improved, and any tendency toward whipping or fluttering is eliminated, by the action of the lands or tongues 75, with the result that the sheets are fully under control at all times.

In operation synchronized means (not shown) are provided for releasing the grippers 12 on the conveyor chain and for engaging grippers 31 of the take-off mechanism which grip the leading edge of the sheet and which decelerate it to a standstill at the forward pile guides 23. During the process of deceleration, the air jet provides a frictional drag on the underside of the sheet which is enhanced by the frictional effect of the tongues 75, with the degree of the latter, depending, as stated, upon the jet velocity. Since the decelerating means operates over a broad area of the sheet, the entire sheet is decelerated without any tendency for the body, or trailing edge, of the sheet to tend to overtake the leading edge, so that the sheet remains flat and free of wrinkling, waving or doubling-over as it settles into place on the top of the pile.

It is to be particularly noted that the structure described above inherently prevents any possibility of intimate contact between the sheet and the nozzle plate 50. The reason for this is that the air which emanates from the nozzle 53 induces a flow of a film of air through an inlet opening 80 at the downstream side of the nozzle plate. This film of air serves to limit the degree of contact between the sheet and the nozzle plate.

Since the braking or drag effect in the present construction is, by its nature, impositive and supplemental, the sheets remain under the control of the front edge grippers 31 and there is no risk that they will be pulled loose even at high jet velocities. The jet velocity, indeed, non-critical and need not be readjusted to follow variations in the speed of the conveyor or take-off mechanism.

While the decelerating means has particular utility when located at a position immediately adjacent the upstream edge of the delivery pile, it is contemplated, in one of the aspects of the present invention, that nozzle-guide plate assemblies may be provided in multiple along the sheet path. For example, a second nozzle and guide plate assembly B, constructed exactly as shown in FIGS. 2 and 3, may be provided along the ascending section of the conveyor for the purpose of holding the sheet in a taut and controlled condition as it changes direction into thefinal leg of its journey free of any tendency toward whipping or fluttering.

With respect to the nozzle-guide plate assembly B, or any other similar unit employed along the sheet path for braking purposes, it will be understood that the term adjacent the pile" is a relative term not requiring immediate adjacency. It will also be apparent that since the assembly may be oriented vertically as well as horizontally (A and B, FIG. 1) the terms above and below, or under, are relative terms; indeed the unit may be operated inverted, if desired, without departing from the invention.

During normal operation and with successive sheets spaced substantially end to end the jet produced from the nozzles is more or less confined, being reduced to relatively low velocity by the time that the air leaves the upstream end of the guide plate assembly. Should there be any discontinuity in the flow of the sheets along the conveyor, means may be provided for automatically cutting off the flow of air so as to avoid unnecessaryair turbulance. Similarly, automatic means may be "provided for turning on the air as the conveyance of sheets is resumed. Response is immediate, whereas devices which relay upon vacuum for braking effect suffer delayed action by reason of the time 'requiredfor the building up of an effective level of vacuum.

It will be apparent that the objects set'forth above have been amply achieved. The assembly is compact, may be mounted at the delivery pile or wherever it is desired along the sheet path and is inherently economical in construction and trouble free in operation.

What we claim is:

1. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets by their leading edges longitudinally along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile-synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating the leading edges thereof for depositing them on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of a sheet so that ajet of air is directed substantially parallel to the underside of the sheet in a direction upstream of sheet movement, a guide plate spaced under the sheet path and extending from the nozzle means in the upstream direction tending to confine the jet of air under the sheet, and laterally spaced land'surfaces interposed between the sheet path and the guide plate so that when the sheet is drawn downwardly by the effectof the jet it engages the land surfaces in light frictional engagement to apply frictional drag to the body of the sheet.

2. The combination as claimed in claim l in which the guide plate is substantially coextensive with the nozzle means and is bent downwardly to flare away from the sheet path in the direction upstream of the sheets.

3. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed parallel to the underside of the sheet in a direction opposite the sheet movement, a guide plate extending from the nozzle means upstream of the sheet tending to confine the jet of air into a well defined layer under the sheet so that the sheet is attracted in the direction of the plate, and friction means interposed between the sheet path and the plate and toward which the sheet is drawn into light frictional engagement to assist in the deceleration of the sheet.

4. The combination as claimed in claim 3 inwhich the friction means extends longitudinally in the upstream direction thereby to inhibit flutter of the engaged sheet.

'5. The combination as claimed in claim 4 in which the plate and friction means are smoothly curved downwardly away from the sheet path in the upstream direction.

6. The combination as claimed in claim 4 in which the longitudinal friction means is in the form of narrow tongues which are smoothly divergent from the plate in the upstream direction and which merge with the plate in the region of the nozzle means.

7. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed parallel to the underside of the sheet in a direction opposite to the sheet movement, a guide plate extending below the sheet path from the region of the nozzle in a direction upstream of the sheets, said guide plate being longitudinally slit at intervals along the width of the sheet to provide divergent upper and lower portions integral with one another, the lower portions, with the underside of the sheet, tending to confine the jet into a well defined layer, the upper portions merging smoothly therewith in the region of the nozzle means and forming tongues for frictional engagement of the sheet as it is drawn downwardly by the jet.

8. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed upstream along the underside of the sheet and in a direction generally parallel thereto, a guide plate under the sheet path and extending upstream from the nozzle means, said guide path having struck-out portions which are spaced along the width of the sheet separated by relatively narrow longitudinally extending tongues, the struck-out portions being smoothly bent downwardly relative to the tongues and together serving to confine the underside of the jet to form it into a more well defined layer under the sheet so that the sheet is attracted toward the tongues for frictional en gagement with the latter, the impingement of the jet and the friction at the tongues combining to decelerate the body of the sheet as the leading edge of the sheet is decelerated by the take-off mechanism.

9. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having an elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of asheet so that a jet of air is directed upstream parallel to the underside of the sheet, a guide plate extending from the nozzle means upstream under the sheet, said guide plate being slit about a three-sided path to form a series of laterally spaced windows defining'struck out portions and frame portions, the struck out portions being bent downwardly from the frame portions so that the struck out portions, taken together, form a lower wall tending to confine the air jet so that a passing sheet is drawn downwardly into at least partial engagement with the frame portions for frictional engagement thereof to assist in deceleration of the sheet.

10. Delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width ofa sheet so that a jet of air is directed in a layer parallel to the underside of the sheet in a direction opposite to sheet movement, thereby to assist in the deceleration of the sheets, the sheet delivery path having successive sections extending along different directions and separate nozzle means for each section to keep the sheet in control as it changes direction between the sections.

1 1. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a sheet delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor including means for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile being synchronized with the arrival of the' sheets for engaging the leading edges of the sheets to remove them from the conveyor and for decelerating the leading edges of the sheets for depositing on the pile,a manifold extending the width of a sheet and located adjacent the pile below the level of the sheet path, the manifold having means for supplying air to it under slight pressure, nozzle means extending along the manifold for receiving air from the manifold and for directing it in the form of a jet parallel to the underside of the sheet and in a direction upstream of the sheet thereby to assist in the deceleration of the body of the sheet, the manifold having compartments arranged end to end, with each of the compartments being connected to the source of pressurized air via a separate conduit, and with means being provided for controlling the flow of air through the conduits thereby to tailor the width of the jet to the width of the sheets being acted upon.

12. The combination as claimed in claim 11 in which the nozzle means is formed by a nozzle plate spaced above the manifold to form an extended nozzle, the plate defining with the sheet an induced air entryway to permit access of incoming air the flow of which is induced by the jet so as to form a film of moving air above the nozzle plate to limit the degree of contact between the sheet and the nozzle plate.

13. In a conveying and delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on thepile, a source of air under pressure having elongated nozzle means, the nozzle means being located below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed generally parallel to the underside of the sheet in a direction opposite the sheet movement, a guide plate extending from the nozzle means upstream of the sheet tending to confine the jet of air under the sheet so that the sheet is attracted in the direction of the plate, and land surfaces interposed between the sheet path and the plate and toward which the sheet is drawn into light frictional engagement to assist in the deceleration of the sheet, the land surfaces being distributed in the width dimension of the sheet and extending longitudinally of the path of travel thereof to inhibit whipping and flutter of the body of the sheet as it is drawn by the conveyor.

14. The combination as claimed in claim 13 in which the guide plate flares in' a direction away from the sheet path for progressive increase in the thickness of the jet. l 

1. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets by their leading edges longitudinally along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating the leading edges thereof for depositing them on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed substantially parallel to the underside of the sheet in a direction upstream of sheet movement, a guide plate spaced under the sheet path and extending from the nozzle means in the upstream direction tending to confine the jet of air under the sheet, and laterally spaced land surfaces interposed between the sheet path and the guide plate so that when the sheet is drawn downwardly by the effect of the jet it engages the land surfaces in light frictional engagement to apply frictional drag to the body of the sheet.
 2. The combination as claimed in claim 1 in which the guide plate is substantially coextensive with the nozzle means and is bent downwardly to flare away from the sheet path in the direction upstream of the sheets.
 3. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed parallel to the underside of the sheet in a direction opposite the sheet movement, a guide plate extending from the nozzle means upstream of the sheet tending to confine the jet of air into a well defined layer under the sheet so that the sheet is attracted in the direction of the plate, and friction means interposed between the sheet path and the plate and toward which the sheet is drawn into light frictional engagement to assist in the deceleration of the sheet.
 4. The combination as claimed in claim 3 in which the friction means extends longitudinally in the upstream direction thereby to inhibit flutter of the engaged sheet.
 5. The combination as claimed in claim 4 in which the plate and friction means are smoothly curved downwardly away from the sheet path in the upstream direction.
 6. The combination as claimed in claim 4 in which the longitudinal friction means is in the form of narrow tongues which are smoothly divergent from the plate in the upstream direction and which merge with the plate in the region of the nozzle means.
 7. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed parallel to the underside of the sheet in a direction opposite to the sheet movement, a guide plate extending below the sheet path from the region of the nozzle in a direction upstream of the sheets, said guide plate being longitudinally slit at intervals along the width of the sheet to provide divergent upper and lower portions integral with one another, the lower portions, with the underside of the sheet, tending to confine the jet into a well defined layer, the upper portions merging smoothly therewith in the region of the nozzle means and forming tongues for frictional engagement of the sheet as it is drawn downwardly by the jet.
 8. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed upstream along the underside of the sheet and in a direction generally parallel thereto, a guide plate under the sheet path and extending upstream from the nozzle means, said guide path having struck-out portions which are spaced along the width of the sheet separated by relatively narrow longitudinally extending tongues, the struck-out pOrtions being smoothly bent downwardly relative to the tongues and together serving to confine the underside of the jet to form it into a more well defined layer under the sheet so that the sheet is attracted toward the tongues for frictional engagement with the latter, the impingement of the jet and the friction at the tongues combining to decelerate the body of the sheet as the leading edge of the sheet is decelerated by the take-off mechanism.
 9. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having an elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed upstream parallel to the underside of the sheet, a guide plate extending from the nozzle means upstream under the sheet, said guide plate being slit about a three-sided path to form a series of laterally spaced windows defining struck out portions and frame portions, the struck out portions being bent downwardly from the frame portions so that the struck out portions, taken together, form a lower wall tending to confine the air jet so that a passing sheet is drawn downwardly into at least partial engagement with the frame portions for frictional engagement thereof to assist in deceleration of the sheet.
 10. Delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located adjacent the pile below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed in a layer parallel to the underside of the sheet in a direction opposite to sheet movement, thereby to assist in the deceleration of the sheets, the sheet delivery path having successive sections extending along different directions and separate nozzle means for each section to keep the sheet in control as it changes direction between the sections.
 11. In a delivery arrangement for a sheet-fed printing press for delivering sheets onto a sheet delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor including means for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile being synchronized with the arrival of the sheets for engaging the leading edges of the sheets to remove them from the conveyor and for decelerating the leading edges of the sheets for depositing on the pile, a manifold extending the width of a sheet and located adjacent the pile below the level of the sheet path, the manifold having means for supplying air to it under slight pressure, nozzle means extending along the manifold for receiving air from the manifold and for directing it in the form of a jet parallel to the underside of the sheet and in a direction upstream of the sheet thereby to assist in the deceleration of the body of the sheet, the manifold having compartments arranged end to end, with each of the compartments being connected to the source of pressurized air via a separate conduit, and with means being provided for controlling the flow of air through the conduits thereby to tailor the width of the jet to the width of the sheets beIng acted upon.
 12. The combination as claimed in claim 11 in which the nozzle means is formed by a nozzle plate spaced above the manifold to form an extended nozzle, the plate defining with the sheet an induced air entryway to permit access of incoming air the flow of which is induced by the jet so as to form a film of moving air above the nozzle plate to limit the degree of contact between the sheet and the nozzle plate.
 13. In a conveying and delivery arrangement for a sheet-fed printing press for delivering sheets onto a delivery pile, the combination comprising means for supporting a pile of sheets, a conveyor for conveying sheets individually along a sheet delivery path to a position above the pile, a take-off mechanism at the delivery pile synchronized with the arrival of the sheets for taking the sheets from the conveyor and for decelerating them for depositing on the pile, a source of air under pressure having elongated nozzle means, the nozzle means being located below the level of the sheet path and extending along the width of a sheet so that a jet of air is directed generally parallel to the underside of the sheet in a direction opposite the sheet movement, a guide plate extending from the nozzle means upstream of the sheet tending to confine the jet of air under the sheet so that the sheet is attracted in the direction of the plate, and land surfaces interposed between the sheet path and the plate and toward which the sheet is drawn into light frictional engagement to assist in the deceleration of the sheet, the land surfaces being distributed in the width dimension of the sheet and extending longitudinally of the path of travel thereof to inhibit whipping and flutter of the body of the sheet as it is drawn by the conveyor.
 14. The combination as claimed in claim 13 in which the guide plate flares in a direction away from the sheet path for progressive increase in the thickness of the jet. 